Solar water heaters similar to the one pictured above are commonplace in warmer climates such as Hawaii. If you were looking into a permenant remote source of warm water that would be the way to go. My current coop is close enough to the house to have ran electric to but for a long time I used two 150' extension cords. I have also used Romex for a short period of time as a long cheap extension cord.
The only other thing I could think of would involve a propane tank and heating element to warm a metal container of water for each use before dispensing it for the chickens.
The only other thing I could think of would involve a propane tank and heating element to warm a metal container of water for each use before dispensing it for the chickens.